Early work demonstrated that 2-butoxyethanol (BE) causes acute hemolytic anemia in rats and that metabolic activation of BE to butoxyacetic acid (BAA) via the alcohol/aldehyde dehydrogenases is a prerequisite for the development of anemia. Studies were designed to compare the sensitivity of various animals (rats, mice, hamsters, rabbits, and guinea pigs) and humans to the effects of the hematotoxic metabolite of BE, 2-butoxyacetic acid (BAA) in vitro. Preliminary results suggested that rats were the most sensitive species while humans were the least sensitive. In another series of studies, the effect of BE on erythrocyte morphology in vivo and the effect of BAA on human and rat erythrocytes in vitro was investigated. Both BE and BAA caused stomatocytosis and vesiculation in rat erythrocytes. In contrast, no such effects were seen in human erythrocytes.